Narrow Results

This work presents a systematic investigation of the corrosion behavior of two materials, 316 stainless steel (316), and Ti6Al4V alloy (Ti6Al4V), in simulated seawater (3.5wt.% NaCl solution). This includes electrochemical tests, immersion experiments, scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) analyses. The polarization curves demonstrate that passivation occurs in both alloys. The lower self-corrosion and passivation current densities of Ti6Al4V indicate that its corrosion resistance is superior to that of 316. However, the impedance spectrum of the 316 shows a larger capacitive arc radius, which is indicative of the presence of a more robust passivation film on its surface. The results of the immersion experiments demonstrate that 316 exhibits a high-corrosion rate under static conditions, which can be attributed to the instability of the passivation film and environmental factors. However, under dynamic conditions, the corrosion rate is lower due to the effect of scouring. In contrast, Ti6Al4V demonstrated superior corrosion resistance in a variety of environmental conditions. In the context of simulated seawater, both 316 and Ti6Al4V exhibited varying degrees of corrosion behavior. Consequently, when selecting corrosion-resistant materials, it is imperative to select suitable materials according to the specific use environment and requirements.

Magnesium-based AX53 alloy was manufactured by a simple stir-casting method. In addition to the standard alloy constituting elements (Ca, Al), elemental Si was added in (0.1, 0.3, 0.6, and 1.0wt.%) during the melting process. SEM and EDX characterized the microstructure and elemental analyses of cast AX53 alloy with/without Si additions, respectively. The effects of Si on the corrosion characteristics of AX53 alloy in 3.5% NaCl have been investigated by weight reduction analysis, potentiodynamic polarization, and electrochemical impedance spectroscopy measurements. The SEM and EDX analyzed the morphology and composition of corrosion products, respectively. Also, the behavior of AX53 alloy with different investigated inhibitors such as nano-TiO₂, nano-ZrO₂, and mixed nano-(TiO₂+ZrO${}_2)$ was assessed. It was observed that the modification of 0.1% Si AX53 alloy by nano-TiO₂ reduces the CR of the alloy. The CR increases with Si additions increasing, generally, the addition of an inhibitor reduces the corrosion rate, and the reductions depend on the type of inhibitor.

Dissimilar welding of duplex stainless steel (DSS) with high-strength low alloy (HSLA) was more complicated since they were utilized in automotive and aerospace design, which needed components with lower weight, higher tensile strength (TS), hardness, corrosion resistance. In this research paper, the main objective was to establish a gas tungsten arc welding process, on a $60^{\circ }$ angle double groove on both sides of DSS and HSLA, using three different filler metals ER2594, ER70S2 and ER304. The welded surfaces of the specimens were analyzed to assess the microstructural characterization using SEM and Edax, and they were also tested to determine their mechanical and corrosion characteristics. In comparison to microstructural characterization, Mn and Si combination decreased the surface defects in the weldment made by ER2594. The determination of mechanical properties revealed that specimen A produced by ER2594 was superior to other specimens B and C, in terms of yield stress, TS and hardness. Similarly, improved corrosion resistance was achieved by the larger presence of Cr along with Ni in ER2594. In the welded joint, Ni combined with an appropriate proportion of other alloying elements in ER2594 enabled effective control over the ferrite-austenite phase balance, which was crucial for achieving the necessary combination of properties and weldability designed for particular applications. Among the three filler metals, ER2594 showed better microstructure uniformity, enhanced TS, hardness and superior corrosion resistance.

This study examined the microstructural, mechanical, and corrosion behaviors of a multidirectional-forged (MDF) Mg–Zn–Ca alloy. The results showed significant grain refinement of the alloy after 5 passes of the MDF process from 378$\mu$m to 23$\mu$m. X-ray diffraction analysis (XRD) revealed the presence of finer Mg₇Zn₃ phases and $\alpha$-Mg and Ca₅Zn₃ phases after the MDF process and peak shift and broadening. Higher hardness ($76.46\pm 3$) was noticed in the MDF 3 pass sample due to grain refinement; further hardness slightly decreased due to texture softening. Moreover, the results of the in vitro corrosion experiments conducted in SBF solution showed that the corrosion current densities of the alloys move in a noble direction as the number of MDF passes increases. MDF 3 pass sample (0.00523mm/y) showed the lowest degradation rates compared to the as-cast sample (0.01154mm/y), attributed to refining and redistributing the second phases.

Four types of coated films (DFT: 300um), that is pure zinc, pure aluminum, and two Al-Zn alloy (Al:Zn=85:15 and Al:Zn=95:5), were coated onto carbon steel (SS401) with arc spraying, and the corrosion behavior of their samples were evaluated by the electrochemical method in this study. The pure aluminum sample had the high corrosion resistance when exposed to seawater solution and pure zinc and alloy (Al:Zn=95:5) samples followed the pure aluminum sample. The other alloy (Al:Zn=85:15), the so-called galvalume that was coated onto the carbon steel, ranked 4th in corrosion resistance in this study. The results of the porosity ratio of those samples are well matched with the electrochemical data

Epoxy resins reinforced by basalt fibers were treated with a sulfuric acid solution for different periods and concentrations. The tensile strength of the composites was examined after the treatment. The fracture surfaces were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The tensile strengths of the sulfuric acid solution-treated samples showed a decreasing trend with treating times and concentrations. However, after 250–500 h of treatment time, the tensile strengths showed an increasing trend. Based on the experimental results, the possible corrosion mechanisms were explored. Sulfuric acid leads to insoluble sulfur oxide formation with high C, Ca and Fe element contents on the fiber surface. With the continuation of sulfuric acid reaction, a thin corrosion shell covers the whole fiber surface. The thickest corrosion shell caused a significant increase in the tensile strength at the breaking of basalt fibers.

Corrosion resistance is of practical importance for the application of 2205 duplex steels in chemical industries. For taking an insight into pitting corrosion behavior, electrolysis was employed to distinguish the 2205 duplex steel samples. In the following, X-ray diffraction, scanning electron microscopy and electron backscattering diffraction are used to characterize the regions with superior and inferior corrosion performance, thus constructing the relationship between the microstructure and their corrosion behavior.

Deposition of phosphate conversion coating using electrochemical methods have many advantages such as low phosphating temperature, low energy cost and good properties of fabricated coating and in recent times increasingly employed for deposition of phosphate coating. Deposition mechanism of coating which is fabricated using electrochemical methods is different from those obtained by conventional chemical methods, consequently, the properties of electrophosphate coating is also different from those conventional phosphate coating. In this paper, recent understanding of deposition mechanism of electrophosphate coating is reviewed. The microstructure, composition, thickness and corrosion behavior of electrophosphate coatings and effect of different factors of those properties were also reviewed.

In this paper, experimental investigation on cryorolled aluminum AA2219-T87 plate by using friction stir welding (FSW) process is carried out. AA2219-T87 plates with a size of 200$\times$100$\times$22.4 mm were rolled and reduced to 12.2mm thickness (more than 45% of reduction in total thickness of the base material) at cryogenic temperature (operating temperature range $-$90–$-$30${}^{\circ }$C). The cryorolled (CR) plates have reduced grain size, improved hardness and increased corrosion resistance property compared with the uncryorolled AA2219-T87 plates. FSW joints of cryorolled AA2219-T87 plates were prepared using cylindrical threaded FSW tool pin profile. Mechanical and metallurgical behaviors of friction stir welded joints were analyzed and the effects of the FSW process parameters are discussed in this paper. The variation of microhardness in the FSW joint regions were correlated with the microstructure of FSW joints. Cryorolled plate and FSW joints were tested for corrosion resistance using potentiodynamic polarization test. FSW joints shows better result during the corrosion resistance analysis compared to base AA2219-T87. The X-ray diffraction (XRD) test results showed that fine $\alpha$-Al grains with eutectic phase (Al₂Cu) were present in the weld nugget (WN). The large clusters of strengthening precipitates were reduced in size and merged with the weld nugget portion.

A pretreatment of sand blasting with the duration of 15min was carried out prior to plasma nitriding for 1045 carbon steel in this study. The corrosion behavior was evaluated by means of electrochemical polarization, electrochemical impedance spectroscopy (EIS) and soaking test, and compared with that without pretreatment of sand blasting. The results show that the pretreatment of sand blasting can significantly enhance the corrosion resistance, the corrosion potential shift to the noble direction, with higher corrosion potential of $-1.067\times 10^3$mV and lower corrosion current of 0.0853$\mu$A/cm², and exhibit larger diameter, higher phase angle and wider frequency region, there exists no corrosion pit after soaking test, and the corrosion rate is decreased from 0.0387g/mm² to 0.01341g/mm², only 1/3 comparing with that of sample without pretreatment of sand blasting. The enhancement mechanism of corrosion behavior is mainly ascribed to the excellent protection from the thicker and denser compound layer with higher amount of $\epsilon$-Fe${}_{2-3}$N.

In this paper, back-propagation (BP) neural network model with 8 hidden layers and 10 neurons was utilized to estimate corrosion behaviors of Ni-TiN coatings, deposited through pulse electrodeposition. Effects of plating parameters, namely, pulse frequency, TiN concentration and current density, on Ni-TiN coatings weight losses were discussed. Results indicated that pulse frequency, TiN concentration and current density had significant effects on weight losses of Ni-TiN coatings. Maximum mean square error of BP model was 9.10%, and this verified that the BP neural network model could accurately estimate corrosion behavior of Ni-TiN coatings. The coating fabricated at pulse frequency of 500Hz, TiN particle concentration of 8g/L and current density of 4A/dm² consisted of fine grains and compact oxides, demonstrating that the coating displayed best corrosion resistance in this corrosion test. Concentrations of Ti and Ni in Ni-TiN coating prepared at pulse frequency of 500Hz, TiN particle concentration of 8g/L and current density of 4A/dm² were 18.6at.% and 55.4at.%, respectively.

In this work, attempt is made to carry out post weld heat treatment (PWHT) on NiTinol samples using laser power source. Initially, 1mm thick NiTinol sheets were welded in butt joint position using Ytterbium: Yttrium aluminum garnet (Yb: YAG) laser power source. Laser welding was carried out in continuous mode, and the quality of the weld was assessed with respect to phase transformation temperatures, microhardness, tensile strength, and corrosion resistance. To improve the quality of the welded samples, PWHT was done by passing a laser beam over the welded samples. It was found that PWHT had a significant effect on the phase transformation temperatures, microhardness, tensile strength and corrosion behavior of the welded NiTinol joints.

Herein, a biomimetic coating of hydroxyapatite (HA)–Al₂O₃ and HA–ZrO₂ was deposited on Ti–6Al–4V-alloy using vacuum plasma spray (VPS) technique. The bond-coat of ZrO₂ has been introduced between the substrate and reinforced HA coatings to study the effect of bond-coat on structural, mechanical properties and electrochemical corrosion performance of the developed coatings. In addition, the impact of thermal treatment of coating was investigated on these properties too. Coating characteristics, such as morphology, porosity, surface roughness, and crystallinity were investigated. The corrosion performance of coatings was tested in Hank’s-based salt solution (HBSS). Significant enhancement in crystallinity and surface-hardness has been witnessed after heat treatment; nevertheless, porosity reduced. The electrochemical corrosion study revealed that the corrosion resistance of heat-treated samples was better than the as-sprayed coatings samples. The intensity of XRD peaks of all coatings increased after 24h immersion in HBSS for the electrochemical test in comparison to the intensity of peaks before the corrosion test.

As a material widely used in aerospace and energy development, the surface quality of nickel and its alloy will need to be improved urgently. Electrochemical polishing, as a surface treatment method, can smoothen the metal surface and improve its corrosion resistance. Strict environmental regulations have given rise to new electrochemical polishing techniques. In this paper, the electrochemical polishing of nickel was carried out using resin particles wetted by deep eutectic solvent (DES) as polishing medium. The surface morphology and roughness of polished nickel were characterized by scanning electron microscopy (SEM) and optical profilometer. In addition, electrochemical polarization curve and electrochemical impedance spectroscopy (EIS) were used to test the corrosion behavior of polished specimens in 3.5wt.% NaCl solution. The results show that the surface morphology of polished nickel shows grain boundary characteristics. The surface roughness Ra can be reduced from 0.612$\mu$m to 0.0913$\mu$m (under 30V voltage polishing 1h), and the corrosion current density can be reduced from 27.30$\mu$Acm${}^{-2}$ to 12.15$\mu$Acm${}^{-2}$. Pitting potential in the polarization curve indicates that the pits at the grain boundaries are corroded due to the influx of corrosive chloride ions. This polishing method combines the resin with DES which can reduce the production of polishing liquid waste while avoiding the use of harmful acid-base electrolytes and effectively reduce the surface geometry uneven degree, improving the surface corrosion resistance.

Nickel super alloys like Inconel 718 characterize a significant metal part in the structures of aircraft and engine components. The high reliability levels are the major conditions during the manufacturing of these essential structural components in aerospace production. Surface integrity is the most important factor considered for estimating the quality of machined surfaces in term of finishing as well as strongly effect on the corrosion behavior of the machined surface. In this study, three-dimensional (3D)-finite element (3D-FE) simulations were accomplished to determine induced residual stresses in machined Inconel 718 alloy. 3D simulations were executed in the sequential successive method using the design of experiments (DOEs) based on Taguchi L₉ technique. Subsequently, a veritable turning was implemented based on the selected Taguchi design to validate the simulation results. Also, the efficiency of independent parameters (cutting speed, feed rate, and depth of cut) on the surface integrity (surface roughness, microhardness, induced residual stresses), and corrosion rate of the machined surface were explored experimentally. Based on analysis of variance (ANOVA), it was obtained that the feed rate is the most relevant factor related to surface roughness and corrosion rate while cutting speed is the most relevant factor related to microhardness and induced residual stresses. The analyzed polarization curves confirmed that the reducing surface roughness and increasing induced compressive residual stresses are robustly related to enhancing the corrosion behavior of Inconel 718. Robust agreement was detected between the predicted and measured data. The optimal values of independent parameters that led to optimal surface integrity and minimum value of corrosion rate were found. Based on the revealed simulation results, the 3D-FE simulation of the turning process afforded consistent data as compared to experimental measurements for the wide range of induced residual stresses.

The corrosion behavior of 16 Mn steel in sodium hydroxide solutions with varying thiosulfate (${\text{S}}_2{\text{O}}_3^{2-}$) concentrations were investigated by salt spray and electrochemical corrosion tests in this paper. SEM, EDS and corrosion weight loss method were used to analysis the corrosion behavior. The corrosion rate increased from 1.0792g·m^-2·d^-1to 1.1699g·m^-2·d^-1 when ${\text{S}}_2{\text{O}}_3^{2-}$ concentration was increased from 3g/L to 7g/L, while corrosion current density rose from 1.114μA/cm² to 2.896 μA/cm² and the capacitive arc radius was reduced. The corrosion products are composed of iron, oxygen and sulfur. The content of O decreased initially and increased upon the addition of ${\text{S}}_2{\text{O}}_3^{2-}$. The presence of thiosulfate was found to accelerate the corrosion of 16 Mn steel in sodium hydroxide solution and the corrosion behavior of 16 Mn steel is notably effected by the concentration changes of ${\text{S}}_2{\text{O}}_3^{2-}$. Furthermore the corrosion rate shows a positive correlation with increasing ${\text{S}}_2{\text{O}}_3^{2-}$ concentration.

Al₂O₃ coatings were prepared on Al6061 alloy substrate under a hybrid voltage by plasma electrolytic oxidation in a silicate electrolyte. Potentiodynamic polarizations tests had been carried out in 3.5wt% (0.6M) NaCl water solutions under static conditions to evaluate the corrosion performance of the coated or uncoated samples. A double-layer Al₂O₃ coating consisted of γ- and α-Al₂O₃, formed upon the Al alloy substrate. It is shown that the Al₂O₃ coatings on Al6061 alloy play roles of anticorrosive coatings, and proper treating time is suitable to enhance the corrosion resistance of the Al₂O₃ coatings.